Liquid aqueous compositions containing surfactants, such as shampoos, liquid soaps, body washes, facial cleansers, other personal care, pharmaceutical and industrial products, typically contain thickeners in order to increase the viscosity of the liquid composition. This enables convenient delivery and handling of the formulated product.
Traditional thickeners which have been used in such compounds include a diversity of anionic, cationic and nonionic synthetic polymers, such as carboxylated and quaternized polyacrylates and polyvinyl compounds. Typical nonionic synthetic polymers include polyvinylpyrrolidone, polyethylene glycol (PEG), and alkoxylated polyols containing lipophilic substituents, such as PEG150 distearate, and ethoxylated methyl glucoside esterified with a fatty acids. Other thickeners which have been used include naturally derived anionic and cationic gums, such as chemically modified cellulose, xanthan gum, tara gum, and guar gum, and a variety of inorganic clays, salts, and electrolytes. A comprehensive list of rheology modifiers is found in the International Cosmetic Ingredient Dictionary and Handbook by T. Gottschalk and H. P. Breslawec, “International Cosmetic Ingredient Dictionary and Handbook,” pages 3974-3977, 14th Edn, Personal Care Products Council Publisher, Washington, D.C., USA (2012). Additional information regarding the physical and chemical mechanisms through which the different thickeners confer viscosity to surfactant compositions is discussed in E. Desmond Goddard, “Principles of Polymer Science and Technology in Cosmetics and Personal Care,” Cosmetic Science and Technology, 1 edition (Mar. 10, 1999), Informa HealthCare, and in “Polymers in Aqueous Media—Performance through Association,” J. E. Glass, Editor, Advances in Chemistry Series No, 223, American Chemical Society, Washington D.C. (1989).
One group of nonionic thickeners includes relatively low molecular weight compounds of various types, such as nonionic alkoxylated surfactants, aliphatic amides, fatty alcohols, hydrophobically modified alkoxylated molecules, which are able to provide increased viscosity to liquid surfactant-based compositions. The mechanism through which these compounds increase the viscosity of aqueous surfactant compositions is thought to be by selective association with the surfactant micelles themselves. These compounds are often referred to as associative thickeners or micellar thickeners because they thicken through association with a surfactant, perhaps through hydrophobic or lipophilic substituents on these small molecules.
Preparation of fatty acid modified, alkoxylated polymers using sugar polyols is disclosed, for example, in U.S. Pat. Nos. 4,252,826; 4,264,478; 4,323,468; 4,324,703; 4,364,930; 4,687,843; 4,708,813; 5,744,062; 6,320,065; 6,727,357; 6,808,701 and 7,297,667 and European patent EP1329255. Alkoxylated glycoside polymers that have been hydrophobically modified with a variety of hydrocarbons are disclosed, for example, in U.S. Pub. Nos. 20010051142; 20020123625; 20020165104; 20030095942; 20030108506; 20030130162; 20030158065; 20030181715; 20030194387; 20040048766; 20040057921; 20040062730; 20040081632; 20040086470; 20040136943; 20050164896; and 20060019861.
One problem with using such compounds as thickeners is that they tend to have characteristics which make them less attractive for use in human personal care products. For example, they are typically prepared from petroleum-derived precursors, and as such are not considered to be environmentally acceptable or renewable materials. In addition, a number of them are ethoxylated compounds. Due to the presence of residual dioxane in the product as result of the preparation procedure, there is a concern about their toxicity. Similarly, aliphatic amines, such as cocamide-DEA and others, can contain residual amines that are believed to form nitrosamines during the shelf life of the product, which are considered to be carcinogens. These conventional thickeners therefore may be unsuited to use in aqueous surfactant-based liquid cleansing compositions for personal care, where the desire is to have as high a concentration as possible of naturally derived or renewable ingredients.
The esterification of polyols, such as sugars or saccharides such as glucose, mannose, galactose, fructose, sucrose, maltose, lactose, starch, cellulose and their derivatives including sorbitol, sorbitane and alkyl polyglucoside, has been studied. Examples of fatty acid esters formed from these sugars are disclosed in PCT applications WO/1992/003060 and WO/2004/031244, where the resulting esters are complex mixtures of polyesters which are used as fat substitutes in food products. As potential thickener components of a surfactant-based personal care composition, however, these esterified materials have some disadvantages. The polyols themselves are typically mixtures of various unstable sugars. Hence, the quality of the resulting esterified product tends to be poor. In addition, the polyol tends to decompose, undergoing significant forms of rearrangement during esterification at temperatures above 130° C., including oligomerization, caramelization or even charring. This results in discolored, dark products containing significant levels of polysaccharides and other intractable species. To address the instability of these common sugars, catalytic enzymes have been proposed, which allow the esterification to be effected under milder reaction conditions, as disclosed in EP 0 507 323. However, the yields of esters using enzymes as catalysts tend to be very low, making them unsuitable for commercial production of such compounds.
U.S. Pub. No. 20120015893 and EP 2 415 454 A1, for example, disclose esters of sorbitan, such as sorbitan sesquicaprylate, in a cleansing composition, such as a shampoo. US Pub. No. 20110092405 discloses surfactant compositions for cleansing formulations thickened with fatty acid esters of glycerol. Both of these polyols suffer from some stability problems.
US Pub. No. 20060024256 discloses the use of fatty amphiphiles in surfactant compositions, but requires the amphiphiles to be incorporated into a dispersed gel network phase to be effective.
The exemplary embodiment provides a micellar thickener suitable as a rheology modifier in surfactant-based compositions.